Conventionally, an airplane comprises two wings that are connected to the fuselage via a central wing box. The function of the wing box is to take up forces coming from the wings and to transmit them to the fuselage.
The building of the central segment of the fuselage thus begins by constructing the central wing box around which the skin elements and the frames constituting the fuselage are added. The box has horizontal top and bottom panels. Each wing has a lateral wing box via which it is fastened to the central box. These lateral boxes also present top and bottom panels. Each top panel of the wings is connected to the top panel of the central box by means of a part that is referred to as a cross or as being cruciform, given the characteristic shape of its section. The same part is also used for connecting the fuselage skin to the central and lateral boxes. Stiffeners of the two panels are also fastened to one another by means of compression fittings.
Unfortunately, the number of parts needed for assembling the wings to the fuselage is relatively high. These operations take place on the final assembly line and they present a duration that is penalizing. In particular, since the box is initially connected to the fuselage, the wings are fastened to the lateral walls of the box, referred to as ribs. This fastening operation is very awkward, given its duration and the number of parts to be assembled together. One of the major lines of present-day research lies in simplifying this junction zone and in redesigning the way in which airplanes are constructed and assembled.